In 1996, more than 75 million people worldwide used cellular telephones. Reliable predictions indicate that there will be over 300 million cellular telephone customers by the year 2000. Within the United States, cellular service is offered not only by dedicated cellular service providers, but also by the regional Bell companies, such as U.S. West, Bell Atlantic and Southwestern Bell, and the national long distance companies, such as AT&T and Sprint. The enhanced competition has driven the price of cellular service down to the point where it is affordable to a large segment of the population.
This competition has also led to a rapid and sweeping innovation in cellular telephone technology. Analog cellular systems are now competing with digital cellular systems. Older frequency division multiple access (FDMA) and time division multiple access (TDMA) systems are now competing with code division multiple access (CDMA) systems. In order to maximize the number of subscribers that can be serviced in a single cellular system, frequency reuse is maximized by making individual cell sites smaller and using a greater number of cell sites to cover the same geographical area. In a typical system upgrade, several existing adjacent cell site are subdivided into multiple smaller sites having different frequency assignments. Care is taken to maximize the distance between cells using the same frequency range. Each of the smaller cell sites may be further subdivided by use of a sectored antenna that splits the cell site into, for example, three 120 degree sectors. The multi-sector, multi-frequency architecture greatly increases the number of users that can be served.
Accordingly, the increased number of base transceiver stations and/or sectored antennas has resulted in increased infrastructure costs. To offset this increased cost, cellular service providers are eager to implement any innovations that may reduce equipment costs, maintenance/repair costs, and operating costs, or that may increase service quality/reliability, and the number of subscribers that the cellular system can service. Much of this innovation has focused on service quality improvements, such as expanded digital PCS services, on user equipment improvements, such as smaller and lighter cellular phone handsets having a longer battery life, or on infrastructure cost reduction, such as smaller, cheaper, more reliable transceivers for the cellular base stations.
Data traffic problems are encountered as cell sites become smaller in conventional wireless architectures. The base transceiver station serving each cell site is usually connected to a base station controller by a T1 line. Each active call being handled by the base transceiver station is assigned to a dedicated time slot on the T1 line. This type of connection has numerous drawbacks. The T1 line has a relatively narrow bandwidth. The base station controller frequently collects from each base transceiver station out-of-performance data associated with the base transceiver station and the active calls it is handling. Performing this function requires a large amount of bandwidth, generally more than the T1 can support simultaneously with on-going voice data transfers.
This problem is worsened by the increased use of high-bandwidth applications by the mobile units. For example, many of the mobile units may be portable computers executing multimedia applications, or video devices, such as video conference equipment. The T1 bandwidth assigned to each mobile unit is simply too small to effectively perform these high-bandwidth applications. The result is that many video applications exhibit a flickering image and many audio applications exhibit a stuttering effect.
There is therefore a need in the art for improved wireless systems that provide reliable high-bandwidth communication links for mobile devices capable of performing multimedia and video applications. More particularly, there is a need for improved wireless infrastructures that provide a guaranteed amount of bandwidth with minimum latency to each active mobile unit.